System for preventing overmodulation in receivers



Sept. 20, 1938. 5. ANDERS' SYSTEM FOR PREVENTING OVERMODULATION IN RECEIVERS Original Filed April 13, 1929 7'0 IYEXI' STA GE 2 Pa 5 Elvwentoz GUIDO ANDERS 3 his W Patented ept. 20, 1938 UETE STATES were SYSTEM FOR PREVENTING OVERMODULA- TION IN RECEIVERS Guido Anders, Berlin-Steglitz, Germany, assignor to Allgemeine Elektrizitats, Gesellschaft, Berlin, Germany, a corpcration of Germany Application April 13, 1929, Serial No. 354,753. Renewed June 7, 1933. In Germany April 25,

The present invention relates broadly to arrangements for controlling the output of amplifying devices.

In receivers comprising several stages of amplification of the kind required for satisfactory reception of distant stations, the amplification is very high so that small signal energies are sufiicient in order to realize optimum modulation of the power stage. However, when such a receiver is located in the vicinity of a local transmitter, the incoming energy is so large that, owing to the high radio frequency, amplification, the power stage is overmodulated. There are two ways to obviate such overmodulation, to wit:

(1)By reduction of the energy transferred to the first circuit.

(2)By reduction of volume by means of subnormal heating (underheating) of the first radio frequency, tube or tubes, or change in grid biasing potential for the radio frequency, amplifier tube or tubes with a consequent shifting of the working point into the negative range (or lower slope),

or into the positive range (artificial damping by grid current).

A reduction of energy transferred to the first circuit may be obtained by loosening the antenna coupling. However, although the antenna coupling can be reduced to zero theoretically, though never in practice, this means is never efiective in the neighborhood of powerful stations in order to avoid overmodulation.

Reduction of volume, as is well known, is accomplished by a change in the filament resistance (series or parallel resistances) or else by an alteration of the grid biasing potential by means of a potentiometer.

Now, the present. invention is concerned with an arrangement in which, by the combined use of these known means in a definite sequence, over- 40 modulation is preventable in a simple and safe manner. In the invention, the antenna couplers and volume regulators (filament resistance, potentiometer) are so designed and interconnected mechanically that when actuating the combina- 5 tion arrangement, first the antenna coupling is made very loose, whereupon, with the coupling remaining loose, the first tube is subnormally heated, or is furnished with another grid biasing potential.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by '5 reference to the following description taken in connection with the drawing in which I have indicated diagrammatically a circuit organization whereby my invention may be carried into efi'ect.

60 In the drawing 26 Claims. (01. 250- 20) Figure 1 is a side elevation of the control device,

Figure 2 shows diagrammatically a circuit including a control device using a potentiometer arrangement as a bias control, and 5 Figure 3 shows diagrammatically a circuit arrangement including the control device shown in Fig. 1, viewed from below and utilizing the system as a filament control.

Therotor-system a of the antenna coupling 10 condenser b is in mechanical coupling relationship with the rotary resistance base d by means of spindle c. The setting wheel (knob) e is fixedly connected-by screws 1, f, with the resistance base d; The based of the filament resistance 15 carries theresistor wire g and a contact bar h, which at one end is in conducting relationship with the resistor wire 9. The filament supply lead 7" is brought to one end of the contact bar h, and the lead It is brought to a contact slide 20 m which slides over theresistor wire 9 or the contact bar h.

The stator system n and the rotor system a of the antenna coupling condenser b are of the quadrant type. The movement of the rotor systerna is limited in both directions by means of a stop pino.

The antenna coupling is the strongest when the two plate systems a,"n. are positioned opposite each other. Upon turning the setting wheel e n in the direction indicated by the arrow, the antenna coup-ling is gradually slackened. After a rotation through an angle of approximately 90 degrees, the coupling is quite loose. The contact spring m of the. heating resistance is then located at the end of-the contact bar it.

Upon continuing the rotation of the setting knob, the resistance is out in the filament circuit. The farther the knob e is turned in clockwise direction, the more resistance will be cut in the filament circuit, and the more will the heating of the filament of the first tube be rendered subnormal. While this reduction in the tube heating proceeds, also the rotor system a of the antenna condenser b will partake of the motion, though no change in the antenna coupling can be produced any more. Upon returning the setting knob e there is first effected an intensified heating of the first tube. After the normal heat ing has been restored, the antenna coupling will be rendered stronger as the rotation is continued. Y

Instead of the filament resistance a potentiometer could also be employed to alter the biasing potential of the first tube as shown in Fig. 2. Fur-7 thcrmcrathe resistance need not necessarily be furnished with a contact bar, indeed, it is surficient to short-circuit the existing resistance turns for the part of the resistance inwhich no change in heating is to be produced. In Fig. 2, the Ire-T sister 9 in series with the contact bar h forms a circuit which is shunted across the filament source A. The grid 'of tube T is-connectedto the brush m through conductor is and coil L. ,It electronic amplifier device connected between said can be seen that rotation of e varies the bias on the tube.

While I have indicated and described only a few systems for carrying my invention into effect, it will be apparent to one skilled in -the.-art that my invention is by no means .limitednto the particular organizations shownand described, but that many more modifications inthe circuit arrangements may be used, as well as in the apparatus employed, without departing from the-scope of my invention as set forth in the appended claims.

What I claim is:

1. In a broadcast receiving circuit an antenna circuit, means for amplifying the radio frequency currents, means in said antenna circuitforvarying the coupling between said antenna circuit and said amplifying means, and-.meana-operative subsequent to said couplingvarying means, for controlling the sensitivity of said amplifying means said two means being operated by a single device.

2. A system for preventing overmodulation of broadcast receivers including radio frequency amplification, which comprises means for gradually varying the coupling between the signal supply circuit of said receiver and said amplification circuit from close coupling'to loose-coupling, means for varying the amplification factor of the radio frequency amplifying circuit and a single means for operating said last two named means successively.

3. A system for controlling the sensitivity of a broadcast receiver to prevent overmodulation when the receiver is locatedin the immediate vicinity of a high power--local transmitterwhich comprises means for graduallyloosening the antenna coupling to approximately zero, and means for inserting a resistancein theinput circult of the radio frequency amplification stage, the variation in the coupling and the insertion of said resistance being effected successively by the operation of a single means.

4. A volume control device for-broadcast receivers comprising, an antenna coupling variable condenser and a resistance adapted to vary the amplification factor of the receiver, a base, a manually operable means connected to said base, means for mounting-said resistanceon said base, a spindle aifixed to said' base; said spindle being adapted to support the rotor system of said coupling condenser, and thevariable element of said resistance and means for. varyingboth said resistance and said condensensuccessively by rotating said spindle.

5. A source of current to beamplified, an amplifying circuit, meansfor varyingithe amplification factor of said circuit, meansfor variably coupling said source to said amplifying circuit and a single means for operating both said amplification factor varying means and said variable coupling means, said operating :means" being I adapted to operate said two means successively.

6. In combination with an electrical signal amplifier having an input. circuit,..an output circuit and at least one space discharge amplifier device interposed between said circuits for the transmission of signals fromsaid: input circuit to said output circuit, means forvarying'the.transmission efficiency of said amplifier device between predetermined limits, andmcans :for'varying the signal strength appliedto said input. circuit,

said two means being variable successively by a single operating means.

7. In combination an electrical signal amplifier having input and output circuits and at least one circuits for the transmission of signals from said input circuit to said output circuit, means for varying the transmission efiiciency of said amplifier device between predetermined limits and means for varying the signal strength applied to 10 said input circuit, said first named means being operative only after the second named means has passed through substantially all of its effective variation range.

8. The combination with an electrical signal 15 amplifier having an input circuit, an output circuit and at least one electron discharge amplifier device connected between said circuits for the transmission of signals from said input circuit to said output circuit, of means provided with .20

an element movable between certain limits to vary the transmission efficiency of said amplifier device, means for varying the signal strength applied to said input circuit, one of said means being operative only after the other of said means. 25

has become operative substantially throughout its effective range of variation.

9. The combination as recited in the next preceding claim wherein the first named means is operative to reduce the transmission efficiency 02 the amplifier device only after the signal strength applied to the input circuit is reduced by the signal strength varying means.

10. The combination with an electrical Signal amplifier having an input circuit, an output cir-. 35

ranged to vary the signal strength applied to said input circuit, the movement of said element being effected to vary the signal strength applied to the input circuit to any substantial degree only over a portion of its range of -movement,' and -means' connected with said movable elements for moving the same simultaneously.

11. The combination with an electrical signal amplifier having signal supply terminals, an input "circuit, an output circuit and at least one electron discharge amplifier device connected between said circuits for the transmission of signals from said with an element movable between certain limits to vary the transmission efiiciency of said amplifier =device, means for varying the signal strength applied to said input circuit from said supply input to said output circuits, of means provided terminals, the last named means including a variable capacity element connected between said source terminals and said input circuit and having a movable control member by which said signal strength is varied, the movement oI'.the

substantial degree the signal strength over a portion only of its range of movement and a common means for moving said elements simultaneously.

.control member being effected to vary in any 12. The combination with an electrical signal 7 amplifier having an input circuit, an output circuit and at least one electron discharge amplifier device connected between said circuits for the transmission of signals from said input mend output circuits, of means having a common control and provided with movable elements for varying the transmission efficiency of said amplifier and the strength of signals received by said input circuit, said movable elements having the same range of movement but different ranges of effective control.

13. In the operation of radio receiving ap paratus utilizing thermionic tubes for amplifying or repeating radio frequency signal energy, the steps in the method of reducing the volume or amplitude of reproduction which comprise lessening the transfer of signal energy to the amplifying tubes and thereafter for further reduction of volume decreasing the amplification effected by the said tubes by modifying their amplification characteristics.

14. In the operation of radio receiving apparatus utilizing thermionic tubes for amplifying or repeating signal energy, the steps in the method of increasing the volume or amplitude of reproduction which comprise increasing the amplification effected by at least one of the tubes by modifying its amplification characteristics and thereafter for further increase of volume increasing the transfer of signal energy to the amplifying tubes.

15. In an amplifier system in combination, a vacuum tube amplifier, means for controlling the bias voltage applied to the grid of said tube, means for controlling the signal input voltage applied thereto and a single means for operating both said control means successively.

16. The method of controlling the output level of a vacuum tube amplifier and increasing the signal to noise ratio which comprises successively adjusting the amplification of the amplifier and the magnitude of the signal voltage impressed upon the same.

1'7. The method of controlling the output energy of a vacuum tube amplifier which comprises successively controlling amplification of the tube and the amount of input signal supplied thereto.

18. In combination with an electrical signal amplifier having an input circuit, an output circuit and at least one space discharge amplifier device interposed between said circuits for the transmission of signals from said input circuit to said output circuit, means for varying the transmission efiiciency of said amplifier device between predetermined limits comprising a variable bias device associated with said space discharge device and means for varying the signal strength applied to said input circuit, said two means being variable successively by a single operating control.

19. In combination an electrical signal amplifier having input and output circuits and at least one electronic amplifier device connected between said circuits for the transmission of signals from said input circuit to said output circuit, a variable biasing device for said electronic amplifier for providing a means for varying the transmission efiiciency of said amplifier device between predetermined limits and means for varying the signal strength applied to said input circuit said first named means being operative only after the second named means has passed through substantially all of its effective variation range.

20. The combination with an electrical signal amplifier having an input circuit, an output circuit and at least one electron discharge device connected between said circuits for the transmission of signals from said input circuit to said output circuit, of means provided with an element movable between said limits to vary the biasing potential on said electronic discharge device and thereby vary the transmission efficiency thereof, means for varying the signal strength applied to said input circuit one of said means being opera tive only after the other thereof has become operative substantially throughout its effective range of variation.

21. The combination recited in the next preceding claim wherein the first named means is operative to reduce the transmission efficiency of the electronic discharge device only after the signal strength applied to the input circuit is reduced a predetermined amount by the signal strength varying means.

22. The combination with an electrical signal amplifier having an input circuit, an output circuit and at least one space discharge device connected between said circuits for the transmission of signals from said input to said output circuit, of means provided with an element movable between said limits to vary the bias potential on said space discharge device and thereby control the transmission efficiency of said device, a second means having a movable element arranged to vary the signal strength applied to said input circuit, the movement of said element being effected to vary the signal strength applied to the input circuit to any predetermined degree only over a portion of its range of movement and means connected with said movable elements for moving the same simultaneously.

23. In the operation of radio receiving apparatus utilizing thermionic tubes or the like for amplifying or repeating signal energy, the steps in the method of varying the volume or amplitude of reproduction which comprise changing the amplification effected by at least one of the tubes by modifying its amplification characteristics and thereafter for further change of volume varying the degree of transfer of signal energy to the amplifying tubes.

24. In combination with an electrical signal amplifier having an input circuit, an output circuit and at least one multi-electrode space discharge device, interposed between said circuits for the transmission of signals from said input circuit to said output circuit, means for varying the transmission efficiency of said space discharge device comprising means for varying the potential applied to one of the cold electrodes thereof between predetermined limits and means for varying the signal strength applied to said input circuit said two means being variable successively by a single operating control.

25. In an amplifier system, in combination, a vacuum tube amplifier, means for controlling the bias voltage applied to the grid of said tube, means for controlling the signal input voltage applied thereto, and a single means for operating both said control means.

26. In an amplifier system, in combination, a vacuum tube amplifier, means'for controlling the amplification characteristics of said tube, means for controlling the signal input voltage applied thereto, and a single means for operating both said control means.

GUIDO ANDERS. 

